Even though there are more Android phones than iPhones in the United States, the number and variety of Android apps lags compared to Apple’s offerings. For instance, Android users had to wait a year before they got Instagram or Pinterest apps. New research helps explain why.

There’s got to be more to the story than the number of phones. Flurry, a mobile-app analytics firm, released a report this week that helps explain the problem, laying out the challenges app developers face. It also shows that Android apps are unlikely to catch up and that small developers coding for either device will get squeezed out of the market.

For app developers to make a decent living, they have to sell 50 apps an hour, 24 hours a day, for $1 each, Johan Emil Johansson, a developer in Sweden, said in a blog post outlining the difficult conditions facing today’s app developers. New app versions are expensive to make, especially in light of the proliferation of devices.

App developers have long had to grapple with an overwhelming number of connected devices. Flurry counted 331 different models of smartphones and tablets that developers would have to code for if they wanted make their apps available on about 90% of devices.

Too ambitious? If developers can content themselves with only 50% of devices in use, the programmers would still have to make versions for 18 different models. And the complexity doesn’t stop there; developers must also adjust apps for different operating systems. For instance, any iPhone 4 user could be running iOS 4, iOS 5 or iOS 6.

But iOS still represents fewer phone and operating system combinations than does Android . And fewer combinations means less development work and testing for cash-strapped programmers.

Flurry also found an even bigger incentive to make an iOS app rather than one for Android: More people will use the apps, and more often.

“Device models running on the iOS platform average 14 times the number of active users compared to device models running on other platforms,” Mary Ellen Gordon, a Flurry analyst, said in a blog post.

In other words, one iPhone user is worth 14 Android users , based on how frequently the apps get used.

And even when Flurry isolated Samsung, the most popular Android device maker, one iOS user was still worth seven Samsung users.

Manufacturers will continue to make new devices in the hopes of standing out from competitors. The last year alone has seen the explosion of the “phablet ,” a phone the size of a small tablet. And the operating system mix of old and new will grow even more complex.

So much for the whiz kid with a quirky, brilliant app idea, like 14-year-old Robert Nay who created Bubble Ball.

“Putting all of this together, we expect a future in which app developers are less frequently individuals with a creative idea and a laptop, and more frequently companies designed to develop, produce and distribute apps at scale,” Flurry said.